Resistance element for variable electrical resistors



July 2, 1935. J. J. MUCHER 2,007,022

RESISTANCE ELEMENT FOR VARIABLE ELECTRICAL RESISTORS Filed Aug. 28, 1934 INVENTOR. JoH/v J. Mac/ ER BY Wrat- A TTORNEYS.

Patented July 2, 1935 UNITED STATES PATENT OFFICE RESISTANCE EmMENr FOR. VARIABLE ELECTRICAL BESISTORS 3 Claims.

This invention relates to variable electrical resistors of the type which embody a resistance element in the form of a film or coating 'of carbonaceous material applied to a flexible non-conductive base such as disclosed in my co-pending application, Serial No. 715,071, filed March 12, 1934 which has since issued as Patent 1,997,427, April 9, 1935.

In variable electrical resistors for use in deli-v cate circuits such as employed as a volume control in radio receiving apparatus, it is essential that the surface of the resistance material be as near flat and as free from irregularities as possible in order to avoid erratic fluctuations or changes in the resistance value.

In variable electrical resistors now in general use, which embody a flexible resistance base in the form of a split ring with'only the terminals thereof secured to the backing, the unsecured portion thereof between the terminals becomes distorted due to the absorption of moisture and the unequal expansion of the opposite surfaces thereof with a consequent warping or buckling thereof away from the backing which warping or buckling of the base and the resistance element thereon produces erratic fluctuations in the resistance when the contact is moved thereover and further frequently resulting in short circuiting.

The present invention, therefore, contemplates an electrical resistor of the type indicated, in which the film or coating of carbonaceous material is applied to an improved non-conductive base which is so constructed and arranged as to prevent buckling, warping or distortion thereof due to atmospheric or other conditions. v

More particularly the invention resides in the provision of a resistance element comprising a thin flexible annular insulation base having a central opening and a coating of resistance material on one surface thereof partially surrounding and spaced from the opening and leaving an uncoated portion defining an insulation surface upon which an annular contact and its terminal element is seated to secure the resistance element in fiat engagement with the backing member so as to prevent flexing or distortion of the resistance element. 1

With the above recited and other objects in view, which will be more fully described hereinafter, reference is now made to the following specification and accompanying drawing in which there is illustrated one embodiment of the invention, while the appended claims cover variations and modifications thereof which fall within their scope.

In the drawing: Fig. 1 is an enlarged inner end view of a variable electrical resistor, with the casing removed, constructed in accordance with the invention.

Fig. 2 is a similar view to Fig. 1 with the rotor it removed.

Fig. 3 is a sectional view taken on a plane indicated on line 3-3 of Fig. 1, and illustrating the same applied to a mounting panel.

Fig. 4 is a perspective view of the improved resistance element.

Referring to the drawing by characters of reference, A designates generally a variable resistor which includes a resistance element B, comprising a thin flexible annular insulation base I of paper or other suitable material, and a carbonaceous resistance material composed of carbon, graphite or a mixture of both, together with a suitable binder which is coated or suitably applied to a portion of one surface of the insulation base in the form of a continuous arcuate strip 9 of a width to extend inwardly from the outer periphery of the base and terminating in an arcuate line ll which line is spaced from and concentric to a central opening II. The continuous arcuate strip 9 also terminates in radially disposed spaced end edges l2 and I3 extending inwardly from the outer periphery of the base to the arcuate line It. This arrangement defines, between the central opening and the inner edge I 0 of the carbonaceous resistance material, an uncoated annular insulation surface portion H and between the end edges l2 and It a radial uncoated insulation surface portion l! forming a continuation of the annular uncoated insulation surface portion H. The resistance element B is disposed fiatly upon an insulation backing I6 to which it is secured by rivets I! or other suitable means of connection and to the terminals l8 and i 9 which project radially from the base, the inner ends of which are disposed upon and in electrical contact with the carbonaceous resistance material.

An annular contact member 20 is secured upon the uncoated portion of the insulation base concentric with the opening and in spaced relation with the resistance material, and is provided with an angulated projection 2| which is anchored to the insulation backing It by a rivet 23 or other securing means. The annular contact member 20 is also provided with a radially projecting anchoring lug 24 which extends through an opening 25 in the uncoated portion ii of the insulation base and is anchored or otherwise secured to the insulation backing IS. The annular contact member 20 thus clamps the resistance member thereby preventing the same from buckling or warping due to atmospheric changes and eliminating distortion of the carbonaceous resistance material.

The insulation backing l6 has secured thereto abushing 26 extending concentrically therethrough with its inner endcrimped over upon the The bushing 26 is formed upper surface thereof. with an enlarged flange 21 between which and the base 16- a washer 28 is interposed, which is keyed or otherwise securedto the bushing 26 to lock the washer against turning movement with reference to the bushing. The washer 26 is provided with a lug 3| which is bent inwardly and is anchored in the insulation backing l6 to hold the backing against turning movement with reference to the washer and bushing 26. The washer is also provided with a radially projecting finger 32 v which is bent at an angle for engagement within the recess 33 in a mounting panel 34 for holding the variable resistor against turning. The bushing is externally threaded and protrudes through an opening in the panel 34 for receiving a lock nut 35 for mounting the variable resistor to the panel. A shaft 36 is mounted for rotation in the bushing 26 and is formed with an annular groove 31 at its point of emergence from the bushing 26, which groove is engaged by a split lock ring"3,8 for limiting the inward axial movement of the shaft. The inner end of the shaft is formed with an annular groove 39 in which groove a rotor 40 of insulation material is arranged. Disposed upon the rotor 40 and arranged in the groove 39 is a Washer 4| which is provided with an offset lu 42 for engagement in an opening 43 in the rotor and by which the rotor is keyed to the shaft 36, the inner end of the shaft being flanged upon the washer 4,2 to firmly secure the washer and the rotor in the groove 39,

The rotor 46 has attached thereto a substantially u -shaped resilient wiper contact 44 disposed in confronting relation with the upper surface of the annular contact member 26 and whichis so tensioned that the intermediate or bight portion thereof frictionally contacts with the said annular contact member. The opposite face of the rotor hassecured thereto a substantially U-shaped contact arm 45, the terminals of which are secured to the terminal ends of the wiper contact 44 by means of conductor rivets 46 which pass through the rotor 40. The contact arm 45 is of greater length than the wiper contact 44 so that the medial or bight portion of the arm 45 overlies the resistance material on the insulation base 8. The

rotor 46 is of generally circular formation, having a radially projecting enlargement 41 which is contoured to define oppositely disposed stop shoulders 48 and 49 adapted to engage with the extension 50 of the'rivet head 23 to limit the turning movement of the rotor and shaft 36. The enlargement 4? is provided with a medial radially disposed-notch 5| which registers with the medial or bight portion of the contact arm 45 and receives an offset tongue52, which is struck from. the bight portion of the arm.

'A non-resilient and non-deformable contact shoe'or element 54 lies partly within the confines of the notch 5| and is provided in the plane upper surface thereof with a groove which receives the tongue 52 of the contact arm 45 so that the said shoe or element 54 is resiliency of the arm 45 into frictional engagement with the resistance on the insulation surface 8. The contact shoe or element 54 is also engaged by the side edges of the notch 5| to be moved by the contact arm 45 in an. arcuate path over the resistance so as to vary the resistance between the terminal 2! and the terminals l8 and I9 res ectively.

What is claimed is:' a I 1. In a variable electrical resistor, a backing member, a resistance element including a flexible annular insulation base having a central openurged by the inherent mg and'a resistance material applied to one surface of. said base and extending partially around the same and spaced'from the central opening thereof to leave an uncoated portion, a contact member engaging against said uncoated portion for clampingly attaching the resistance element vidingannular and radial uncoated insulationsurface portions against which uncoated surface portions the annularfixed contact and radial terminal thereof are impinged to hold the resistance element in applied contact with the backing mema thin flexible annular insulation base. I

ber so as-rto prevent" flexing or distortion of the resistance element. l 6

3. In a variable electrical resistor, a' rotatable shaft, a backing member fixedly secured concentrically with reference to theshaft, a resistance element comprising an annular insulation base of thin flexible paper having a central opening and a coating of resistance material on one surface thereof in the formof a continuous arcuate strip extending inwardly from the periphery of the base and terminating in an arcuate line spaced from and concentric with the central opening and de-I fining between the central opening and the arcu-. ate inner edge of the coated strip, an annular un-. coated surface portion, an annular contact member overlying saiduncoated surface portionand secured to said backing member with ,the insulation base fixedly suppor-tedupo nthe backing member concentric with said shaft, a resilient wiper contact, and a movablecontact element mounted for movement by andiwith said shaft for engagement respectively with, said annular contact member and said resistance material for varying the electrical resistance.

JOHN J. MUCHER. 

